Abrasives



United States Patent ABRASIVES John R. Gregor and Harold E. Van Orden, Tiifin, Ohio, assiga'ors to Abrasive & Metal Products Co., Detroit, Mi'cl1'.','a corporation of Michigan No Drawing. Filed Mar. 11, 1957, Ser. No. 644,973

8 Claims. '(Cl. 51-298) -"The present invention relates generally to the production of abrasives and more particularly to the production of grinding wheels for heavy duty use such as in snagging in'jthe steel industry, and the like.

'I'his 'application'is a continuation-in-part of our application, Serial No. 503,795,filed April25, 1955, and now Patent Serial No. 2,811,430.

In the'production of abrasives a mixture of abrasive gains and a bond material including fillers, binder resin, plasticizers and other ingredients are combined and molded in various ways. The filler in a molded abrasive is-believed to reduce cutting temperatures, preventloading of the-surface of the abrasive, and to otherwise improve-cutting efiiciency. The filler material usually employed is 'a-finelyground or' powdered natural mineral known as cryolitef having the general formula Na AlF Even though cryolite significantly improves the cutting efiiciency of grinding wheels, in the grinding of stainless and alloy-steels the performance of cryolite-filled grinding wheels has left something to be desired. Moreover, since cryolite'is largely imported, its supply and priceare subject to wide fluctuations in times of international crisis.

It is an object of this invention, therefore, to provide an abrasive article which contains an inexpensive, readilyavailable filler or fillers and which has an efficiency at least equal to that of cryolite.

Another object is to provide a filled abrasive article which .will morefgsatisfactorily grind stainless steel and othertough alloy steels, Still other objects and advantages of .the present invention will be apparent, or will becomeapparent, in the more specific description of the invention tofollow. V I, A In accordance with the present invention an abrasive article is provided containing at least one filler selected from the class consisting of the alkali metal salts of sulfuric, hydrochloric and hydrobromic acid and mix tures of at least one of the latter salts with antimony sulfide. Most of these fillers orcombinations of fillers areinexpensive and readily available in large quantities at all times. With combinations of the alkali metal salts and antimony sulfide in certain proportions, synergistic effects are noted, that is, the combination is much more effective than either of its components when used alone andan abrasive article is produced which is capable of cutting faster and which has longerlife than heretofore known comparable abrasive articles manufactured for similar purposes. The abrasive articles of this invention are most efiective in the cutting or grinding of stainless and alloy steels.

While we do not Wish to be bound by theory due to the fact that the function of fillers is imperfectly understood, the following explanation is offered only because it appears to fit the facts as presently known. The stainless alloy steels and various of the other alloy steels high in total alloying ingredients, are characterized by their toughness and abrasion resistance. Consequently, grinding pressures and/or grinding times, must be increased to remove a given weight of metal, as compared to iron ice or mild steels. Consequently, the abrasive wheels wear away at an increased rate and temperatures generated at the metal-to-abrasive interface will usually be higher and may, in fact, be so high that a thin surface layer of the metal itself may be burned, oxidized, or otherwise heat-modified to'make it unsightly. The high temperatures may cause the heated metal to load the wheel and reduceits cutting efficiency. Likewise, the bond material, and particularly the filler content thereof, may be modified, volatilized or otherwise rendered inefiective at the temperatures obtained. We have observed that many materials which have melting points above about 1200 C.-are not' effective as fillers in abrasives for grinding the alloy steels. This might-indicate that a good filler has a fiuxing, protective or other function and that such function requires a liquefaction of the filler. Further support for-the latter surmise is furnished by the observation that many of the mostefiective mixtures or combinations of fillers of the invention either are at or near their eutectic composition, orare compositions exhibiting lower meltin'g points than one or both of its components used alone. It is believed that the sulfur of the sulfides is dissolved by the .molten alkali metal salts to form a low melting fiuxing composition that greatly facilitates grinding.

The abrasive articles of this invention may be any molded abrasive made from a mixture including abrasive grains and a bond material containing one or more of the above fillers and a resinous thermosetting binder material. The abrasive articles of this invention which are'particularly efiective are molded abrasives having ahigh' density, thatis,an abrasive article having a low per centage of void spaces (i.e. less than 15%). It is the latter type that is utilized in heavy duty grinding such as snaggingi- Any' abrasive grain or mixture of grains may be employed including silicon carbide, boron carbide, tantalum carbide, tungsten carbide or other hard metal carbides; alumina such as emery, and including electric furnace-fused alumina such as corundum, diamond grains, glass, quartz, garnet, etc. The "resinous binder material in the bond material must be curable, heat-hardenable or heat-convertible to form a hard, strong bond which will not readily deteriorate at elevated temperatures. An illustrative binder resin found particularly satisfactory in the abrasives of this invention is the fusible B-stage phenolic resins '(phenolaldehyde or cresol aldehyde resins which are available in either powdered or liquid form. If desired, the heat-convertible binder resin can be modified with small proportions of other 'res inous or,rubbery materials such as the epoxy resins, vinyl resins including those of vinyl chloride, vinyl butyral and-others, styrene-acrylonitrile resins, butadieneacrylonit-rile rubbers, and others and may contain varying proportions of cross-linking or curing agents such as hexamethylene tetram-ine, paraformaldehyde, and others. In some cases solvents or plasticizers such as furfuraldehyde, propylene sulfite, furfuryl alcohol, cresol, and others may-be present in the bond mix, if desired. The bond mix may also contain, in addition to the fillers of this invention, any of the conventional fillers and other ad ditive materials such as cryolite, feldspar, iron oxide, andothers; -If desired the bond may also contain lime, and I where furfuraldehyde is employed, the presence of lime. is recommended.- I i I The mixture of this invention which is molded may contain any operable ratio of abrasive to bond although, in general, for heavy duty grinding wheels the mixture will usually contain from about 54 to about 64% by volumeof abrasiveandfrom about 36% to about 46% by volume ofthe bonding materiah'it being understood that the bonding material so specified includcs the Binder resin, fillers, plasticizers and other added'non-abrasivein gredients. An illustrative abrasive wheel mixture may contain from' about 54% to. about 64% by' volume of abrasive, from about. 16. to about 26% by volume of I binder resin or resins, frorn about 1% to about 4% by volume of lime, from about 8% to about 20%"of total filler, and from '0 -to'200 ml, of furfuraldehyde forevery poundtof' powdered phenol-'alclehyde'resin, if the latter 'type is employed.

' filler andin no case shouldithe'proportiom oftthexfillers' of the present invention constitute lessfthan: about" 2%? by volume of the total, bonding material.

tional cold- 'or hot-pressing methods may be employed wherein the abrasive grains are first wet with furfuraldehyde or another plasticizer or solvent and the binder resin, liars, and other dry, powdery or liquid ingredients then added to the wet-ted grains and mixed until homogeneous. The resulting damp mixture then is placed in either a hot or cold mold and pressed under high pressure to form a-coherenr green abrasive which is removed from the mold and hearted [in an oven to cure the bond. The displacement methodrdisclosed the co pending 'appiicat'iorr of John Gregor and -samnel L. Kistler, Serial No; 499,443; filed April 5, 1 955,1and now Patent Serial No. 2,86 0;9"6 l',' may also be employed to advantage. In the lafitermetlfo'd," dry, loose'abrasi've gnains are placed in a suitable mold and a continuous layer of a fluid or fluidized bond" mix applied to one exposed surface of the grain layer in the mold. Air is removed or is permitted to escape from the surface of the a In combination with-antimony sulfide,. any oithe alkali metal salts of sulfuric, hydrochloric and hydrohromic. acids may be employed as fillers: int-the abrasivesof this invention including those of-lithium, sodium, potassium, rubidium and. cesium. Illustrative salts of. thisetype include sodium sulfate, potassiumsulfate, lithium. sulfate; cesium, sulfate ((35 304); rubidium. sulfate (Rb sOg),

sodium. bromide, sodium chlo1ide;..pot assium bromide,,

potassium, chloride, and many others. AlLofthe-known alkali: metal; salts of these acids. melt. at. temperatures hea low about 1100 Ct and many'of themore common salts 7 10f. "this type melt at temperatures between 4Q0- C..;to about..900 C. Of these, thezsodiumandrpotassiumz sub: 1 fates, sodium' andpotassium chlorides, and sodium: and.

potassium bromides are; most readily available, are less expensive and 'havebeenfoundtoibe very efficientfillers when used in admixture withantimony sulfide;

' When'. antimony sulfide is added to. the abrasive: along withone or mor e of; the metal salts-,, ,a greatiireprovernentrinthe cutting efliciency of the resultingz-abreu sive is usually noted. This'is surprising sincev antimony I sulfide, when. used 'as .a sole'filler, either, producesaabrasives; which are much. poorerlincutting'efiiciency, on no 1 moregefficient thancryolitee As littleas '5.%Ito.-'10%:

antimony sulfideby volume; based .onithei'total volume of; alkali; metal and antimony sulfidefiller, significantly improves: cutting efiiciency. In mostthe-pro.-

portionof sulfide is increased, largeincreasesinrcuttingefficiency are; realized until a; point is reached-where furs 7 thei increases; in. cutting elficiency areqnotiobtained.

.For'examplq with mixtures of'antimony sulfide and sodi um; sulfate, potassium. chloride, sodium. chloride, potase slum: bromide; and sodium bromide, the-maximum cut-1 ting efiiciency is obtainedwithmixltures of about 50%- antimony sulfide and 50,%' of the salt by volume, based on, the .total' volumeofi thealkali metal and: antimony sulfidefillers. When potassium sulfate isemployed as the..salt the maximumjcutting efiiciencytoccurs. at mixtures of antimonysulfide and: 75 potassium. sill-- fatc,. .bu1..the cuttingel'ficiency' is' substantially; atzits maxi-1 mumtuntilamixture of.7 5% antimony sulfid'e and. 25% potassium. sulfate is' reached. Increases in; antimony.

'suilfide. above about175 with the balanceione ofthe.

above. named, decreases thecuttingi-jefliciency.

The cutting efliciency remains better thamthatobtain abletwithcryolite as the sole-filler. until theeproportion of antimony sulfide is 85% 'ofihetotal filler: Statediin terms-.015.- ratio;jabrasives.-having; snagging grinding char acteri'stics superior-"Ito that. obtainable: with. cryolite can 7 Barnacle with. a. ratio ofantimony sulfidevtozralkalirmetal saltwithin; therrange .of.,5;6:1 to about 1:7;

r abrasive products. of this; inventiorr;;can1be1-.madeconventionalimanner; Eor: example; the-conven grain layer oppositethe continuous bond layer to produceaflooding, directional movement of the bond layertoward theopposite surface to ensure completefilling. of the voids. Gravity, vacuum, gas pressure, or centrifugal force may be applied to one-side or the other ofthe abrasive layer to increase the speed of the directional movement of the bond. The abrasive is then baked-t0 cure the bond. Any other method maybe employed 'which is capable of. producing a sound, compact, wellbonded abrasive article.

The invention will now be described int-greater detail in connection with a number of -illustrative specific examples; Unless otherwise specified inthe examples, all proportions-will be expressed as percent by volume.-

A plurality of seriesof abrasive wheels were madeby the cold pressing technique using a mixture.- containing by volume ofabrasive and approirim-ately 38%10' 40% byvolume of bonding material includingplasticizer. The bonding material. hadthe following general 1 comi position, by volume:

Powdered B-stage phenol formaldehyde' resin Lime a 8 Fi ller' 27 inure dry abrasive grains tliere was first added cc.

of .furluraldehyde, forevery piound' ofbinder resin to be employed; The I liquidiand' abrasive" were then 1 a-unifo'rmaconsistency was ob'tained; Tlie'povfdered bonding-materials were first co'r'nl'j'iued' with 30 cc. of the equivalent of a neutral tar', oil before-being added to'the somewhat moist mixture of abrasive and, furfuraldehyde.

Mining'was then until'a'homogeneousmixture was obtained. Wheelswere rrradeifrom this mixture by eold'pressin'gs r t V a V "Each series of 'wheels included four-"control' wheels which contained powdered pryolite' as the sole Four other control wheels were made employing-anti mony sulfide as'tlie solefiller audfour'additional fillers were made employing-the selected alkali metal salt as thesole filler. Four wheels'were'1uad'e containihga 'mixture; of antimony sulfide and the selected alkali met'al salt, constituting the entire filler, in' the proportions-of of about 250 lbs: per square" inch," which is typical" of pressures commeroiaily'employedin such opera tions; Thedatapresented in tabular'cform below=repre= sents: the 'average'of' the results obtained the four Wheels:- f v slain-sat sbgs, with KCl Wheel Steel Filler Wear, Removal, S/W Q in lhr. lbs.

813283 Na2SO4 Wheel Steel Filler Wear, Rfirnoval B/W Q Wheel Steel Filler Wear, Removal, S/W Q in. /hr. 5.

43. 82 33. 36 761 82. 8 57. 47 37. 98 661 75. 6 75 KOl/25 SbzS 40. 89 35. 46 867 102. 5O KCl/5O Sb2S3 34. 71 35. 84 1. 061 133. 0 25 KCl/75 $1233.... 40. 98 40. 14 980 121. 9 SbgS; 38. 15 26. 58 697 55. 7

Sb S with NaCl Fill gheel R Ste 1 S/W Q er ear, emova in; lhr lbs.

Steel Removal, SIW Q number Q is expressed in the equation Qz "W s where W is the loss in weight of the wheel in cubic inches per hour, S is the pounds of steel or metal removed per hourand C C and K- are constants. The value of these constants was determined by plotting the results of several hundred grinding tests using the conditions above specified with cryolite filled wheels and calculating the value of the constants from the plotted line. "Ihe constants C C and K so determined are 5549', 6000 and 136, respectively. The above Q values were all calculated using these constants.

It may be seen from an inspection of the above examples that the combination of antimony sulfide with each of the alkali metal salts illustrated gives 8/ W values and Q values which are greater than the corresponding values for cryolite alone, or antimony sulfide alone and in all cases except potassium sulfate, greater than the alkali metal salt alone. In making comparative grinding tests, many variables may afiect the actual results obtained and in order to obtain reliable comparison figures it is necessary to utilize wheels which have been manufactured on the same day and cured at the same time or under identical curing temperature conditions. Moreover it is necessary to do all of the grinding of any one test on steel obtained from one batch. In all of the above tests these conditions were followed so that the relative figures within a specific test are meaningful but it should be understood that because of the variations which may occur in the steel being ground, the conditions of wheel manufacture or the conditions of operation of the testing equipment, it is not reliable to draw conclusions by comparing one set of test data against another. For example in the above data relatively wide numerical variations exist between the S/ W ratios for the antimony sulfide control wheels employed in the potassium bromide and sodium bromide tests relative to similar Wheels employed in the other tests and yet the data is reliable, on a comparison basis, in its own particular test.

What is claimed is:

1. An abrasive article comprising abrasive grains and a bonding material, said bonding material comprising a thermosct binder resin and a filler, at least one half of said filler consisting of at least one alkali metal salt of sulfuric, hydrochloric and hydrobromic acids in admixture with antimony sulfide, said admixed filler constituting at least about 2% by volume of the total bonding material and the ratio of antimony sulfide to said alkali metal salt being within the range of about 5.6 to 1 to about 1 to 7.

- 2. An abrasive article in accordance with claim 1 wherein said admixed filler consists of potassium sulfate and antimony sulfide.

3. An abrasive article in accordance with claim 1 wherein said admixed filler consists of potassium chloride and antimony sulfide.

4. An abrasive article in accordance with claim 1 wherein said admixed filler consists of potassium bromide and antimony sulfide.

5. An abrasive article in accordance with claim 1 wherein said admixed filler consists of sodium bromide and antimony sulfide.

6. An abrasive article in accordance with claim 1 wherein said'admixed filler consists of sodium sulfate and antimony sulfide.

7. A cured molded abrasive article comprising abrasive grains, a thermosct phenolic binder resin, and a'filler consisting essentially of a mixture of antimony sulfide and at least one metal salt of sulfuric, hydrochloric and hydrobromic acids in which the ratio of antimony sulfide to said alkali metal salt is within the range of about 5.6 :1 to about 1:7, said admixed filler constituting at least about 2% by volume of the total bonding material.

8. A cured molded abrasive article comprising abrasive grains, a thermoset phenolic binder resin and a filler consisting essentially of a mixture of antimony sulfide and at least one alkali metal salt of sulfuric, hydrochloric and hydrobromic acids and in which said antimony sulfide is present in an amount of from 5% to by volume of 

8. A CURED MOLDED ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS, A THERMOSET PHENOLIC BINDER RESIN AND A FILLER CONSISTING ESSENTIALLY OF A MIXTURE OF ANTIMONY SULFIDE AND AT LEAST ONE ALKALI METAL SALT OF SULFURIC, HYDROCHLORIC AND HYDROBROMIC ACIDS AND IN WHICH SAID ANTIMONY SULFIDE IS PRESENT IN AN AMOUNT OF FROM 5% TO 85% BY VOLUME OF 2% BY VOLUME OF THE TOTAL BONDING MATERIAL. 